The present invention generally relates to a compound for dentistry and, more precisely, it relates to a dental composition for the treatment of dentinal hypersensitivity.
In particular, the composition is suitable for the desensitization of the exposed dentin, such as, in particular, for
the desensitizing treatment of deep cavities,
the desensitizing treatment when replacing dental layers,
the stumps desensitizing treatment before placing dental prosthesis.
The composition can be used as a solution or as a gel.
Dentinal hypersensitivity is a problem often met by dentists in their patients and is often intensified when eating hot or cold food, sweet or acidulous food, as well as when brushing teeth.
Normal dentin is covered by enamel (crown dentin) or by cement (radicular dentin) and is not permeable.
In teeth sensitive zones enamel is found often eroded or worn away and dentin exposed. In other cases, gingival recession uncovers the most sensitive portions of the teeth, i.e. the junction enamel-cement.
The absence of cover exposes the dentinal tubules. In addition, pulp is rich of nerves many of which are centrifugally directed towards dentin. Dentin is crossed radially by dentinal tubules which contain dentinal fluid. Through the tubules a nervous stimulus reaches sensorial areas of the dental pulp.
A first known way to reduce dentinal sensitivity is to close the orifices of dentinal tubules. To this extent, natural substances are known able to reduce sensitivity by closing the tubules, such as tartar, collagen or mineral salts precipitated in saliva.
Chemical compounds, like solutions, gel compounds to or pastes, as well as physical treatments are also known capable of mechanically obliterating the orifices of the dentinal tubules. Compounds of the s kind are known in GS2239601 and in WO 92/04006.
Other compounds or treatments or this kind are:
potassium and iron oxalate, which react with ionised calcium present in the saliva and form calcium oxalate which Precipitates and obliterates the dentinal tubules orifices;
silver nitrate which acts through the precipitation of silver compounds;
tin fluoride, which acts through the precipitation of tin compounds;
strontium salts;
insoluble salts such as calcium phosphate, hydroxyapatite, colloidal silica etc. which directly obliterate the tubular orifices;
glass-ionomeric cement;
some types of resins.
Other compounds, known for example in U.S. Pat. No. 5,603,922 or in WO-A-97/06774, provide a composition useful to remineralize lesions in dental enamel. Hypersensitivity is counteracted as a secondary effect, owing to the obliteration of dentin due to remineralization.
In any case the obliteration of the dentinal tubules by means of soluble or insoluble salts used up to now, even if they are simple to use, is not enough effective and last only a short time.
Compounds are known, moreover, such as potassium chloride or nitrate or oxalate capable of reducing the dentinal sensitivity through a depolarising effect of the nervous fibres, without obliterating the dentinal tubules. Therefore, desensitization treatments are known using said compounds, capable of stopping the pulpal nervous activity by varying the dentinal tubules nervous fibres excitability. However, also in this case, the effect duration is short.
New techniques, not yet used in clinical practice, use glass-ionomeric cement or photo-induced resins. Desensitization is improved, but they are not easy to use and are good for deep erosions only.
Moreover, treatments are known using either laser or ultrasounds scalers, which cause the formation of smear layers and tubules obliteration. These treatments give results, such as effectiveness and duration, similar to the topical treatment with the above described soluble or insoluble salts, but they require expensive apparatus.
It is an object of the present invention to provide a dental composition for dentinal desensitization which has good mechanical obliteration properties of the dentinal tubules in addition to depolarising properties of the nervous dentinal fibres, arid is capable of obtaining good effectiveness and long duration, as well as of being easy to use.
According to a first aspect of the invention, this object is reached by the composition whose characteristic is to comprise at least two solutions to be used successively on the exposed dentin.
A second aspect of the invention provides at least two distinct gel compounds to be used successively on the exposed dentin.
The characteristics of said solutions and said gel compounds is to comprise a first and a second solution or a first and a second gel, suitable for being mixed topically, wherein:
in the first solution a first solute consisting in potassium phosphate and at least a second solute selected among potassium carbonate, potassium fluoride, potassium oxalate, are present, and
in the second solution a first solute selected among a calcium salt and at least a second solute selected among a strontium salt, a silver salt, a barium salt, a zinc salt are present,
whereby a crystal complex is formed comprising
a plurality of insoluble salts having obliterating properties on the dentinal tubules obtained by double exchange reaction of the first and second solute of the first and second solution,
a soluble potassium salt having depolarising effect on dentin.
The preferred general weight ratio for the firs solution is the following:
The preferred general weight ratio for the second solution is the following:
The preferred general weight ratio for the first gel compound is the following:
The preferred general weight ratio for the second gel compound is the following:
The combined use of the two preferred solutions or of the two preferred gel compounds successively has the result, after an immediate double exchange reaction, of six insoluble salts:
calcium phosphate,
calcium carbonate,
calcium fluoride,
strontium phosphate,
strontium carbonate,
strontium fluoride,
and a soluble salt, i.e. potassium chloride.
According to a sudden reaction a xe2x80x9ccrystal complexxe2x80x9d is formed by said six insoluble salts which surprisingly have shown desensitizing properties in the short term (15 minutes) and in the long term (6-12 months).
The formation of the potassium chloride helps to increase the desensitization properties adding a nervous depolarising effect. In fact, potassium chloride is obtained after a double exchange reaction and is present in solution inside the dentinal tubule when the xe2x80x9ccrystal complexxe2x80x9d is formed which obliterates the tubules orifices. In this way a higher amount of potassium is present for a longer time with respect to the depolarising compounds according to the prior art, which do not obliterate the dentinal tubules, thus allowing the dentinal fluid (whose flow is always centrifugal) and then also the potassium ions to come out the dentinal tubules.
The use of an induced crystallisation for obliterating the dentinal tubules with the formation of a xe2x80x9ccrystal complexxe2x80x9d along with the formation (always inside the tubules) of a compound with depolarising properties of the nervous fibres, is new in the dental field, and is used with excellent results according to the present invention.
If the composition according to the invention is prepared with potassium phosphate, potassium carbonate and potassium fluoride (for the first solution) in amounts higher than 20, 10 and 5% respectively for the first solution and with calcium chloride and strontium chloride in amounts higher than 20 and 11% respectively for the second solution, a desensitizing is obtained having the same good properties as above described, but less convenient to use. In fact, at the moment of the union of the two solutions, when the formation of the six insoluble salts occurs, an opalescent gel compound would result, less handy and less spreadable on the surface to cure.
It is also advisable that the two solutions are spread with different brushes so that the two solutions or gels are not in contact before they reach the patient""s mouth.
Similarly, the composition with potassium phosphate, potassium carbonate and potassium fluoride in amounts higher than 10, 5 and 0.5% for the first gel compound and with calcium chloride and strontium chloride in amounts higher than 10% for both the salts of the second gel compound, a desensitizing composition is obtained which can be used having the same properties as above described, but less suitable for a toothpaste because its organoleptic aspect would be less acceptable.